Question

When a screw gauge with a least count of 0.01 mm is used to measure the diameter of a wire, the reading on the sleeve is found to be 1 mm and the reading on the thimble is found to be 27 divisions.
(i) What is the diameter of the wire in $cm$?
(ii) If the zero error is +0.005 cm, what is the correct diameter?

Answer 1

Reading $=$ Linear scale reading $+$ (coinciding circular scale $\times$ least count)

$=0.1+(27\times 0.001)$

$=0.127cm$

True diameter $=$ observed diameter $-$ zero error

$=0.127-0.005=0.122cm$